Main Bearing Oil Clearance Question ..

[Rosco_NZ]

So I was told the crank was fine, in spec at STD, mains & B/E’s. And I’ve had the case prepared at another machine shop, case halves decked flat & tunnel align bored back to STD. The engine builder has just called to say he has installed the main bearings and torqued the through bolts and there is too much clearance for STD bearings ... how?????

[stownsen914]

How much clearance? Also, which bearings are being used?

[Rosco_NZ]

Glyco mains. About .1mm excess I think. Engine builder suggest .25mm under bearings and grinding the crank .. I’d rather not. I’ve heard it may be possible to mix bearing sets to get the right clearance ..??

[r lane]

The bearings can be coated to take out .001''. If your crank is not new, I

[r lane]

can't imagine that it is 100% standard anywhere. I am surprised that the case work didn't close things up.

[targa72e]

Measure the bores in case with out the bearings and compare to spec. If bores in case are not in spec send back to machinist.Sounds like crank already measured OK. If the mains are in spec it sounds like a problem with bearings.

john

[stownsen914]

.1mm is .004". If it's off by that much, someone f'ed up somewhere. If the crank main journals are under spec, sometimes it's better to find a good crank. I always forget which of the non-standard bearing sizes are the unobtanium ones, but some are really expensive.

[Rosco_NZ]

I think the crank mains are at the lower end but still in std spec. I think it is the case machining to focus on. They’re a well known mag case specialist and paid good money so pretty disappointing if that turns out to be the source of issues.
I’ve heard Glyco bearings can have some problems but usually BE’s ...

[stownsen914]

If a freshly machined case is over by .1mm (.004"), that's really inexcusable. That's a huge amount to be off. Definitely take that up with the machinist.

As for bearings, correct that Glyco rod bearings are the ones that seem to have had issues in recent years. Builders I've spoken to seem to still use them for mains (but measure to check). For later engines, there is an option to use GT3 bearings which I believe come in several color coded size variations for "standard" size, but I'd guess the differences are on the order of ten thousandths of an inch.

[mikedsilva]

Originally Posted by Rosco_NZ

I think the crank mains are at the lower end but still in std spec. I think it is the case machining to focus on. They’re a well known mag case specialist and paid good money so pretty disappointing if that turns out to be the source of issues.
I’ve heard Glyco bearings can have some problems but usually BE’s ...

hi Rosco
who did you get to machine the case? I'm looking for a shop to do mag cases for me too. Pm me if you like?

Mike

[Rosco_NZ]

I’m reading about Calico CT-1 dry film lubricant .. it seems it may be possible to coat the bearings with CT-1 to close up the clearance by 0.1mm .. anyone had experience doing this and its success?? The process would need to control applied thickness very closely .. Is this accurate enough??

[356RS]

I have used Calico CT-1 on a few engine rebuilds. Had all the bearings coated. My thought was to help prevent a little of the bearing ware on first start-up and the first few 1K miles. It's a coating and will ware off after while. If your using the CT-1 for a 0.10mm + clearance issue, it won't last to long.
Just my opinion.

[r lane]

Unless Calico has come up with something new, you will close it up by .001'' or .025mm

[drgouk]

Originally Posted by Rosco_NZ

I think the crank mains are at the lower end but still in std spec. I think it is the case machining to focus on. They’re a well known mag case specialist and paid good money so pretty disappointing if that turns out to be the source of issues.
I’ve heard Glyco bearings can have some problems but usually BE’s ...

Hi Ross,
Where in the tolerance of 62.00-62.019 was the main tunnel with the case torqued? (measuring with a bore gauge, No bearings fitted, apart from the nose bearing)